Appliances such as washing machines and dish washers, include one or more frequency modulated signal sources. Examples of frequency modulated signal sources include, but are not limited to, liquid level sensors. The liquid level sensors may include capacitive plates submerged in a liquid. As a level of liquid changes, the capacitance also changes. Further, a capacitance-to-frequency converter senses the varying capacitance and generates a signal, for example a square wave signal having a frequency that is inversely proportional to capacitance. Thus, the information of the liquid level is encoded in terms of the frequency of the square wave signal.
Such frequency modulated signals can be decoded either by a microcontroller or by an integrated circuit (IC) dedicated for that purpose. For example, a frequency-to-voltage converter may be used to convert the frequency modulated signal into a DC voltage. The DC voltage thus obtained is linearly proportional to the measured capacitance and is thus indicative of the liquid level.
Generally, several bytes of memory are consumed by coding instructions, which are written in the microcontroller, to decode the frequency modulated signals. In addition, extra lines or cables are required to interface the microcontroller with the liquid level sensors. The burden becomes even more pronounced in complex applications where the microcontroller has to attend to critical tasks as well. On the other hand, dedicated ICs that are used for the purpose of decoding frequency modulated signals are not just complex to implement, but are also cost ineffective. In addition, the ICs occupy a substantial fraction of the board real estate.